JP3211129B2 - Frame phase synchronization method between base stations - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiple access / time division two-way communication system (TDM) using the same frequency in both directions.
A / TDD) and a time-division multiple access / frequency-division two-way communication system (TDMA / FD) using different frequencies in both directions.
The present invention relates to a method for synchronizing frames between base stations in a mobile communication system using D).

[0002]

2. Description of the Related Art FIG. 1 shows a time division multiple access / time division bidirectional communication system (TDMA / TD) using the same frequency in both directions.
D) or a time division multiple access / frequency division bidirectional communication system (TDMA / F
1 schematically shows a mobile communication system using DD). In this system, it is necessary to synchronize TDMA frames transmitted from the base station 1 and the base station 2, respectively.

Since a plurality of radio stations transmit and receive signals at the same frequency at a time (slot) specified for each station within a predetermined cycle (frame), the start of each frame is started. It is necessary to match the time for all stations, and this is performed by a common master clock. This is T
This is called phase synchronization of a DMA frame, and each station needs to transmit a signal in a designated slot in the frame. That is, it is necessary to synchronize the phases of the TDMA frames transmitted from the base station A and the base station B in FIG. 1 and transmit a signal (referred to as a burst signal) to each station in the frame within a predetermined time. .

FIG. 6 shows a conventional TDMA / TDD system or a frame synchronization system between base stations in the TDMA / FDD system. Control signal transmitted from base station 1 (burst 1-slot signal transmitted at certain intervals)
Is intercepted by the base station 2 and a phase detection level 19 for detecting the transmission timing of the base station 1 is set to a constant level in advance, and the phase detection level 19 is obtained from the output signal of the demodulator 10 after the envelope detection of the intercepted signal. At the detection level, the comparator 12 performs phase detection. Here, the computer 16 corrects the time difference β between the transmission timing of the intercept signal from the base station 1 detected by the comparator 12 and the actual transmission timing of the base station 2, and obtains the base station 1 and the base station 2 obtained as a result. Thus, frame synchronization between base stations is achieved by determining the optimal transmission timing from the time difference between the transmission timings of the transmission signals, that is, the phase difference between the transmission frames. α is the difference between the transmission timings of the base stations 1 and 2.

FIG. 7 shows a method of measuring the time difference β between the transmission timing detected from the intercept signal and the actual transmission timing. As shown in the figure, the control signal transmitted from the modulator in the own base station is received by the demodulator 10 and the output after the envelope detection is input to the comparator 12 in which the phase detection level 19 is previously set to be constant. Then, the counter 14 measures the time difference between the transmission timing detected by the comparator 12 and the actual transmission timing output from the modulator 18. The measurement result is defined as a time difference β.

[0006]

In a system in which a predetermined phase detection level is set in the conventional frame synchronization method between base stations, as shown in FIG. 8A, when the level of the intercept signal is constant, Since the time difference β between the timing of the comparator output signal and the actual timing of the interception signal in FIG. 7 is constant, the time difference of the transmission frame with respect to the counterpart base station, that is, the phase difference can be accurately calculated, and the stable base station can be calculated. Inter-station frame synchronization can be established.

However, when the state of the transmission line changes with time as in the case of mobile communication as shown in FIG. 8 (2), the level of the intercept signal also changes at the same time, and the deviation of the time difference β between the transmission timings increases. . As the deviation increases, each burst-like control slot signal deviates from a predetermined position (timing) in the frame, and the problem of interference between transmission signals also develops.

[0008] An object of the present invention is to shift the burst-like control slot signal from a predetermined position (timing) in a frame due to a change in the level of an intercept signal as described above.
An object of the present invention is to provide a frame synchronization method between base stations which solves the problem of interference, and reduces a control error due to a change in a reception input level.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, a feature of the present invention is to provide at least two base stations and a TDM.
In mobile radio communication in which bidirectional communication with a mobile station is performed by the A / TDD system or the TDMA / FDD system, a control signal is periodically transmitted by using a frequency of at least one control channel in a plurality of base stations in a time division manner. A base station intercepts a control signal transmitted from another base station, detects a frame phase thereof, and determines a transmission timing of a control signal of its own base station. A base station intercepts a control signal transmitted from another base station, and determines that a control signal has been received when the output after envelope detection of the intercepted signal exceeds a phase detection level predetermined by a comparator. The detected time is detected as the transmission timing of the interception signal, and the time difference between the transmission timing of the interception signal detected by the comparator and the transmission timing of the control signal of the own base station, that is, the transmission frame The phase difference measured by counter,
The base station has means for detecting the reception input level of the control signal of another base station, and the counter measures the time difference between the transmission timing detected by the comparator of the intercepted signal and the actual transmission timing at the reception input level by the counter. The value obtained by subtracting from the phase difference between the transmitted frames is used as the frame phase difference between the base stations, and the transmission timing of the base station and the timing of the received signal do not overlap and the difference between the timings is TDMA / TD.
D or the inter-base-station frame synchronization method that determines the transmission timing of the control signal of the own base station so as to be n (n = 1, 2,...) Times one transmission slot length of TDMA / FDD.

[0010]

According to the present invention, the time difference between the transmission timings of the transmission signals of the respective base stations calculated based on the intercept signal while the phase detection level is fixed, that is, the phase difference of the transmission frame is determined by the reception input level. The main feature is to correct the phase difference. The difference from the conventional technique is that the phase difference of the transmission frame calculated based on the intercept signal is corrected by the reception input level.

The time difference between the transmission timings of the transmission signals of each base station calculated based on the intercept signal, that is, the phase difference between the transmission frames can be corrected in accordance with the reception input level. It is possible to establish a stable frame synchronization between base stations by sufficiently following the fluctuation of the reception input level.

[0012]

FIG. 2 illustrates a frame synchronization method between base stations according to a first embodiment of the present invention (1). The same reference numerals as those in FIG. 6 indicate the same components. FIG. 4 is a diagram for explaining a method of measuring the reception input level A. As shown in FIG. 2, the control signal transmitted from the base station 1 is intercepted by the base station 2, and the output of the intercepted signal after the envelope detection is passed to a comparator 12 having a phase detection level V (constant). Next, the output of the comparator 12 and the base station 2
, The time difference between the transmission timings of the transmission signals of the base station 1 and the base station 2, that is, the phase difference γ of the transmission frame is obtained. On the other hand, as shown in FIG. 4, the output after the envelope detection is passed through an integrator, and the averaged level is converted into a duty ratio (1 / 2k when the number of transmission slots is k in the TDMA / TDD system, TDMA / FDD). In the system, the reception input level is obtained as a value multiplied by the reciprocal of 1 / k when the number of transmission slots is k. Then, as shown in FIG. 3, a time difference between the transmission timing detected from the intercept signal and the actual transmission timing, that is, a correction amount t is obtained from the following equation,
The value α obtained by subtracting the correction value t from the phase difference γ of the transmission frame is defined as the phase difference of the transmission frame between the two base stations.

The following shows the relational expression among the correction value t, the reception input level A, and the phase detection level V.

Here, C is the equivalent capacitor value of the envelope detector, and R is the resistance value.

[0015]

(Equation 1)

Based on the phase difference α of the transmission frame between the two base stations obtained as described above, the transmission timing of the base station 2 and the transmission timing of the base station 1 do not overlap and the difference between the timings is TDMA / TDD. Or TDMA / FD
D, one slot length n (n = 1, 2,...)
The transmission timing of the transmission signal of the base station 2 is determined so as to double the transmission timing. N of one slot length (n = 1, 2,...)
By making it twice, the timings of the control signals transmitted from the base station 1 and the base station 2 do not overlap, and interference can be prevented.

In this manner, stable frame synchronization between base stations can be established without being affected by fluctuations in the reception input level.

FIG. 5 is a diagram for explaining another method for measuring the reception input level A. As shown in FIG. 2, the control signal transmitted from the base station 1 is intercepted by the base station 2, and the output of the intercepted signal after the envelope detection is passed through a comparator having a phase detection level V (constant). Next, from the output of the comparator 12 and the transmission timing of the base station 2, the time difference between the transmission timings of the transmission signals of the base station 1 and the base station 2, that is, the phase difference γ of the transmission frame is determined.
On the other hand, as shown in FIG. 5, the output after the envelope detection is obtained as a reception input level A at the time when the pulse level is stabilized after a sufficient time t has elapsed from the start point of the pulse of the control signal. Then, as shown in FIG. 3, the correction amount t of the phase difference between the transmission frames of the base station 1 and the base station 2 is obtained from the following equation, and the value α obtained by subtracting the correction value t from the phase difference γ of the transmission frame is calculated by the two base stations. And the phase difference between the transmission frames.

The following shows the relational expression among the correction value t, the reception input level A, and the phase detection level V.

Here, C is the equivalent capacitor value of the envelope detector, and R is the resistance value.

[0021]

(Equation 2)

Based on the phase difference α of the transmission frame between the two base stations determined above, the transmission timing of the base station 2 and the transmission timing of the base station 1 do not overlap, and the difference between the timings is TDMA / TDD. Or TDMA / FD
D, one slot length n (n = 1, 2,...)
The transmission timing of the transmission signal of the base station 2 is determined so as to double the transmission timing. N of one slot length (n = 1, 2,...)
By making it twice, the timings of the control signals transmitted from the base station 1 and the base station 2 do not overlap, and interference can be prevented.

By doing so, stable frame synchronization between base stations can be established without being affected by fluctuations in the reception input level.

[0024]

As described above, according to the present invention, the transmission timing of the control signal to be newly transmitted by the own base station is determined each time in consideration of the transmission timing of the control signal transmitted by the adjacent base station. It is possible to maintain a stable transmission timing without being affected by the fluctuation of the reception input level due to a change in the state of the transmission path due to fading or the like.
High quality service can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a system to which the present invention is applied.

FIG. 2 is a schematic diagram of a frame synchronization method between base stations when the present invention is implemented.

FIG. 3 is a diagram illustrating an envelope detector and illustrating a method of calculating a phase difference correction value from a received input level when the present invention is implemented.

FIG. 4 is a view for explaining a method for measuring a reception input level in the embodiment of the present invention.

FIG. 5 is a view for explaining another method for measuring a reception input level in the embodiment of the present invention.

FIG. 6 is a schematic diagram of a conventional frame synchronization method between base stations.

FIG. 7 is a configuration diagram for obtaining a reference value of a time difference between a comparator output timing and an actual transmission timing.

FIG. 8 is a diagram illustrating a problem that occurs in a conventional frame synchronization method between base stations.

[Explanation of symbols]

 Reference Signs List 10 base station 2 demodulator 10a envelope detector 12 comparator 14 counter 16 computer 18 base station 2 modulator 20 reception input level measurement circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 102 H04Q ^7/ 00-7/38

Claims (3)

(57) [Claims] 1. At least two base stations and TDMA /
In mobile radio communication in which bidirectional communication is performed with a mobile station using a TDD system or a TDMA / FDD system, a control signal is periodically transmitted using a frequency of at least one control channel in a time-sharing manner by a plurality of base stations. A base station intercepts a control signal transmitted from another base station, detects a frame phase of the control signal, and determines a transmission timing of a control signal of the base station. The station intercepts a control signal transmitted from another base station, and determines that a control signal is received when an output after envelope detection of the intercepted signal exceeds a phase detection level predetermined by a comparator. The determined time is detected as the transmission timing of the interception signal, and the time difference between the transmission timing of the interception signal detected by the comparator and the transmission timing of the control signal of the own base station, that is, the transmission frame The base station has means for measuring the phase difference with a counter and detecting the reception input level of the control signal of another base station. The transmission timing detected by the comparator of the intercept signal at the reception input level and the actual transmission A value obtained by subtracting the time difference between the timings from the phase difference of the transmission frame measured by the counter is used as the frame phase difference between the base stations. The transmission timing of the base station does not overlap with the reception signal timing, and the difference between the timings is TDMA. / TDD or n (n) of one transmission slot length of TDMA / FDD
= 1, 2,...) Times the control signal transmission timing of the base station itself. 2. A duty ratio (TDMA / TD) of an intercept signal, wherein a reception input level of a control signal from another base station is converted into a value obtained by passing an envelope detection output of the received control signal through an integrator.
When the number of transmission slots is k in the D system, it is 1/2.
k, the number of transmission slots in the TDMA / FDD scheme is k
Is detected as a value multiplied by the reciprocal of 1 / k).
The method for synchronizing a frame between base stations according to claim 1. 3. The reception level of a control signal from another base station is changed from the start point of the pulse of the control signal after the envelope detection of the received control signal, and the level of the pulse is stabilized. 2. The method of synchronizing a frame phase between base stations according to claim 1, wherein the phase is detected as a pulse level at a time point.